Free · No sign-up · Every step of the math shown
Know the size before you buy.
One question per tool, answered with the official chart or method behind it. Mini splits, generators, pools, water heaters, insulation and more. If a number isn't published, the tool says so instead of guessing.
How every tool works
- The size comes from a government or standards source, quoted on the page.
- Every step of the math is shown, line by line.
- Product specs come from the maker. Blank means they don't publish it.
- When the official method runs out, the tool says so and points you to a pro.
The tools
- SplitSizerWhat size mini split do I need?Tool 01 · Mini split
- GenSizerWhat size generator do I need?Tool 02 · Generator
- PoolSizerHow many gallons is my pool?Tool 03 · Pool gallons, pump, heater
- TanklessSizerWhat size tankless water heater do I need?Tool 04 · Tankless water heater
- TankSizerWhat size water heater do I need?Tool 05 · Tank water heater
- AtticSizerHow much attic insulation do I need?Tool 06 · Attic insulation
- DehuSizerWhat size dehumidifier do I need?Tool 07 · Dehumidifier
- ACSizerWhat size window AC do I need?Tool 08 · Window and room AC
- SoftenerSizerWhat size water softener do I need?Tool 09 · Water softener
- WattSizerWhat size power station do I need?Tool 10 · Portable power station
Why these exist
Most "what size do I need" answers online come from the brand selling you the bigger one. These tools use the published chart or method instead, show the math, and tell you when the honest answer is "get a pro to run the numbers".
How they're paid for
Some tools show "check price" buttons. Those are affiliate links: if you buy through one, Foundry NW may earn a commission at no extra cost to you. It never changes the size a tool recommends.